Protein kinases represent a large family of enzymes, which catalyze the phosphorylation of target protein substrates. The phosphorylation is usually a transfer reaction of a phosphate group from ATP to the protein substrate. Due to their activity in numerous cellular processes, protein kinases have emerged as important therapeutic targets.
Epidermal growth factor (EGF) is a widely distributed growth factor that in cancer, can stimulate cancer-cell proliferation, block apoptosis, activate invasion and metastasis, and stimulate angiogenesis (Citri, et al., Nat. Rev. Mol. Cell. Biol. 7:505, 2006; Hynes, et al., Nat. Rev. Cancer 5:341, 2005). The EGF receptor (EGFR or ErbB) is a transmembrane, tyrosine kinase receptor that belongs to a family of four related receptors. The majority of human epithelial cancers are marked by functional activation of growth factors and receptors of this family (Ciardiello, et al., New Eng. J. Med. 358: 1160, 2008) so that EGF and EGFR are natural targets for cancer therapy. The human epidermal growth factor receptor (HER) tyrosine kinase family consists of four structurally related cellular receptors: the epidermal growth factor receptor (EGFR; HER1), HER2 (ErbB2), HER3 (ErbB3), and HER4.
EGFR inhibitors erlotinib and gefitinib as well as the dual EGFR/HER2 inhibitor lapatinib are FDA-approved cancer drugs that are effective against multiple solid tumor cancers. However, their effectiveness is also limited by the drug resistance that frequently emerges following treatment. Point mutations in the kinase domain of EGFR as well as upregulation of by-pass signaling pathways are frequently observed resistance mechanisms in patients treated with gefitinib and erlotinib. A single point mutation at the gatekeeper position, T790M, in EGFR kinase domain accounts for approximately 50% of acquired resistance.
Thus, the compounds that can inhibit mutant protein kinases such as EGFR-T790M activity with improved efficacy or overcome drug resistance are highly desired.